1. Field of the Invention
The present invention relates to a display device, a viewing angle control device, and an electronic device, and more specifically to a display device which can switch to a mode in which an image to be viewed changes depends on the viewing direction and which can detect which position on a display screen is touched by a pen or a finger, a viewing angle control device, and an electronic device.
2. Description of the Related Art
The weight of electronic devices has recently been reduced, with the result that electronic devices with displays, such as mobile phones and mobile PCs, can now be used in public spaces. This, however, has induced such a problem that a person around the user can peek a confidential document and personal information.
To solve this problem, there is proposed a display device which is usually set in a wide viewing angle display mode and can be set in a narrow viewing angle display mode when the display device is used in a public space. In the narrow viewing angle mode, a normal image is viewed from a position right in front of the display where the user is positioned, whereas a solid color image or an image different from the normal image is viewed from a position in an oblique direction to the display. Moreover, since the wide viewing angle display mode is available, a wide viewing angle is obtained when, for example, a large number of persons view an image which has been taken.
In the meantime, various types of electronic devices adopting a touch sensor and a touch panel, which are input devices detecting a position where a finger, a pen, or the like touches, have recently been in widespread use.
A touched position is detected by known methods such as an electrostatic capacitive coupling method, a resistant film method, an infrared light method, a supersonic method, and an electromagnetic induction/coupling method. Among these methods, the resistant film method has widely been adopted. According to this method a position is detected in such a manner that two transparent resistant films are provided to face each other and these films are in contact with one another at a position where a pen or the like touches one of the films.
In case where a touch panel is combined with a display, the touch sensor capability is achieved by, for example, providing a touch panel in front of an image display section such as a liquid crystal display panel. A touch panel adopting the resistant film method is combined with an image display device in such a manner that, two transparent resistant films are pasted together to form a resistant sheet and this resistant sheet is pasted onto the front surface of the image display device. Patent Document 1 (Japanese PCT National Phase Unexamined Patent Publication No. 56-500230; published on Feb. 26, 1981) and Patent Document 2 (Japanese Laid-Open Patent Application No. 2003-66417; published on Mar. 5, 2003) disclose a basic device of a touch panel adopting the electrostatic capacitive coupling method.
In case where a touch sensor is combined with one of various types of electronic devices by pasting a touch panel onto the front surface of the electronic device, the transmittance of light from the display device is reduced because the touch panel is provided on the display screen of the electronic device, i.e. provided between a displayed image and the user, and hence the display quality is deteriorated. The transmittance of light is particularly low in the case of a touch panel adopting the resistant film method, because air with a different refractive index exists between two resistant films.
Furthermore, the addition of a touch panel increases the total thickness and weight of the device. Providing a touch panel on an electronic device is also disadvantageous in terms of cost reduction.
The same problems occur also in a case where a touch sensor is provided in the aforesaid display device which can be switched to the narrow viewing angle mode.